The present invention is directed to an arrangement for preventing air from contacting molten metal during discharge thereof through refractory plates of a sliding closure unit.
When producing steels such as aluminum-killed steels, for example, it is desirable that during the teeming of the molten steel no air comes near or into contact with the discharged molten metal flow. Therefore, for the pouring of molten steel by means of slide gate nozzles, it has been proposed ("Vesuvius Advanced Technology Systems") to provide in one of the two abutting respective sliding surfaces of the refractory plates of the sliding closure unit a groove or recess which, as a closed configuration, encircles the discharge opening. This groove or recess is charged with an inert gas, such as argon, such that only argon can pass forward into the vacuum spaces created between the sliding surfaces by the discharged flow of molten metal, thereby to prevent contamination of the quality and composition of the metal. Admittedly, such a groove or recess provided as a closed or endless configuration around the discharge opening functions optimally if placed sufficiently close to the discharge opening. However, such positioning does not allow sufficient plate material in the area of the discharge opening for the wear of the discharge opening or of the sliding area.
It also is known, as disclosed in West German DE-AS 24 17 490 to provide abutting sliding surfaces of a sliding closure unit with U-shaped grooves or recesses having free or branch ends directed toward each other, such ends of the recesses overlapping each other and forming a closed loop encircling the discharge opening in all positions, i.e. both the open and closed positions, of the sliding closure unit. Gas under pressure, for example an inert gas, is supplied to the closed loop formed by the overlapping grooves or recesses. This arrangement is provided to prevent infiltration of the molten metal between the refractory plates, which infiltration would block the sliding closure unit. It is assumed that under the influence of a relatively high ferrostatic pressure, particularly involving the use of high capacity steel teeming ladles, the molten steel will find its way into the pores of the plates and/or spaces between the sliding surfaces of the plates when the ferrostatic pressure is higher than the opposing capillary pressure. Although not mentioned in such West German document, the prevention of metal infiltration by means of a pressurized inert gas supplied to the grooves or recesses implies that the flowing stream of molten metal is shielded from atmospheric air, as is the case in the above discussed first-mentioned known arrangement. However, the greatest danger of metal infiltration occurs when the sliding closure unit is in the closed position, so that it is in this position that greatest care must be taken to ensure that the gas pressure in the grooves or recesses stays above the ferrostatic pressure. In other words, in this known West German arrangement, the grooves must overlap when the plates are in the closed position.